Data from the pilot program's first month shows most riders board between midnight and 3 a.m. at stops near nightlife like Girard Avenue, 2nd Street, 13th Street and 40th Street on the Market-Frankford Line and AT&T Station, Walnut-Locust and Lombard-South on the Broad Street Line.

But the increased ridership has not offset the additional cost.

"The overnight service has so far been pretty popular among riders who already use SEPTA," Smith said.

To put a dent into the extra expenses, SEPTA needs people who normally take taxis or other modes of transportation home to hop on the train, which has not been the case so far.

"There hasn't been any significant difference in drivers' earnings since SEPTA starting running the 24-hour [weekend] subway line," said Ronald Blount, president of the Taxi Workers Alliance of Pennsylvania. "From what drivers have been telling me, it's been pretty much the same."

SEPTA will determine the future of overnight service on the Broad and Market-Frankford lines after the pilot ends Nov. 2.